Method for cutting paper and other graphic supports on a roll at the same time along two perpendicular axes with automatic correction of errors

ABSTRACT

A method of cutting, simultaneously on two axes (X, Y) perpendicular to each other, of a sheet or web of paper and other graphic or photographic substrates ( 10 ) with series of images, comprising the steps of feeding forward the substrate sheet or web ( 10 ) to a direction (F), detecting the speed of sheet or web ( 10 ) feed and the speed at which the distance is varying between image reference marks ( 11 ) and the ideal feed direction, determining a correct cutting line (T X ) in a transverse direction to the feed direction (F) of the sheet or web by data processing according to trigonometric relations through a microprocessor to obtain the angle of parallelism defect of the image with respect to the ideal feed forward direction, aligning suitable mobile means ( 4 ) of transverse cutting with the desired cutting line (T X ) by means ( 5 ) for shifting the transverse cutting means.

The present invention relates to a method of automatic cutting, on twoperpendicular axes simultaneously, of paper and other graphic substrateswound in roll, provided with automatic correction of errors due toskiddings of the substrate, particularly for substrates printed withdigital rendering systems and for large formats, either provided withlateral reference marks, external to the image, or lacking anyadditional reference mark.

The technology of cutting such printed substrates has been limited todeveloping cutters being able to cut along the two axes, but havinggreat limits. In particular it was impossible to correct skiddings ofthe roll, if badly re-wound, or inaccuracies due to the image itself, ifprinted not perfectly parallel to the edge of the substrate. Further, itwas impossible to cut along the X-axis, parallel to the image inhorizontal direction, if due to one or both the above-mentioned reasons,this side, when cut, is not perfectly at right angles with the papercutter.

Due to the ever increasing market-penetration of the digital printing,which is replacing the offset technology thanks to its flexibility andreduced costs for short runs, there has been a great increase of theprocessed volumes, whereby the manual finishing is no more acceptableand it is thereby essential to automatize the finishing of the prints.In addition, while for small formats the consequences of possibleskiddings of the roll or of the image can be unimportant, in largeformats these are not acceptable and their correction becomes essential.

The co-pending international patent application PCT/IT2006/000198 in thename of the same applicant discloses a device allowing to makeautomatically a precise cutting of graphic substrates in roll, on bothlongitudinal and transverse directions, comprising a system for thecorrection of the cut direction depending on possible deviations of thesubstrate. However, with the device according to that application thereis the need of providing reference marks on the graphic substrate, to berecognized by suitable optical sensors in order to determine thecorrection of the cutting path in a direction transverse to the forwardmovement of the graphic substrate, and standard lateral reference marks(two black bands and an intermediate white one) which can be detected byan optic cell to carry out the longitudinal cut at the correctlocations.

An object of the present invention is thus to overcome the limits of theprior art for what concerns the possibility of obtaining the same resultof substrate cutting without any need of reference marks, for cutting ina transverse direction to the forward movement of the substrate, or ofstandard lateral reference marks, external to the image, to carry outthe cut in longitudinal direction.

This object is achieved with a cutting method having the characteristicsspecified at least in claim 1, with possible further aspects, optionalor preferred, resulting from the dependent claims.

An advantage of the method according to the present invention is thepossibility of detecting, as reference mark, very different kinds ofdelimitation lines between zones having a sufficient contrast withrespect to each other, such as the image edge, when the contrast betweenthe colour of substrate and that of the image edge is sufficient for theoptic cell to detect the image edge itself, or the edge of the paper orsubstrate when it can be considered substantially parallel to the imageedge.

Other objects, advantages and characteristics of the method according tothe invention will result more clearly from the following detaileddescription with reference to a device suitable to carry out the methodof the invention, as represented schematically by way of non-limitingexample in FIG. 1.

The cutting method, simultaneously on two axes (X,Y) perpendicular toeach other, according to the present invention comprises a stepconsisting in feeding forward in a direction F a web or sheet 10 ofpaper or other substrate being fed from a roll, such as by means ofcounter-rotating rollers 1.

FIG. 1 shows a device adapted to accomplish the cutting method accordingto the present invention, comprising a pair of rollers 1 (only the upperroller of which is shown) and a motor 2 for their drive, to feed forwarda web or sheet 10, being fed by a roll in the direction of arrow F.

In another step of the method, suitable detecting means 9, such as anoptic cell, detects the positioning of reference marks 11, beingprovided on the web 10 to determine the location where the cut inlongitudinal direction T_(Y) has to be made. In the method according tothe present invention these reference marks 11 are delimitation linesbetween areas having a sufficient contrast with respect to each other.These delimitation lines may be lateral reference marks of various kind,such as single or multiple lines printed parallel to the image edge; maybe the image edge itself when the contrast between the colour of thesubstrate web or sheet 10 and that of the image edge is sufficient forthe detecting means 9 to detect the image edge; or may be the edge ofthe web or sheet 10 when it can be considered substantially parallel tothe image edge.

In a subsequent step of the method suitable means 8 for shifting means14, 14 a of longitudinal cut are controlled by a microprocessor (notshown) in order to shift to a direction F″, transverse to the directionF of feeding forward the web 10, the longitudinal cutting means 14, 14 aand to render their position coincident with the correct direction oflongitudinal cut T_(Y).

The detecting means 9 can be e.g. mounted on the longitudinal cuttingmeans 14, 14 a.

In a preferred embodiment the longitudinal cutting means 14, 14 a areformed of two or more rotating blades located above the substrate 10 tobe cut and finished along cutting lines T_(Y) provided for (there may beat least another cutting line at the center of substrate 10 when theimages are printed in pairs in side-by-side relation along the X-axis).Said rotating blades 14 a, being driven in any known way by a motor 7,are mounted at predetermined positions, according to the dimensions ofthe images to be cut, on a single shaft movable transversally and drivenby shifting means 8, such as a motor.

Once determined the correct cut lines T_(Y), a step of longitudinalcutting is carried out along said cut lines T_(Y) by means of the abovementioned longitudinal cutting means 14, 14 a.

In the cutting method according to the present invention the feed speedsof web 10 are detected as well the speed at which the distancevaries-between the reference marks 11 of the image and the ideal feeddirection, whereby the angle of parallelism defect is evaluated, throughprocessing based on trigonometric relations, carried out by themicroprocessor.

According to the present invention suitable mobile transverse cuttingmeans 4 are brought into alignment with the correct cut line T_(X)through means 5 for shifting the transverse cutting means 4 which arepositioned at an angle, with respect to the feed direction, which iscomplementary to the angle of parallelism defect, i.e. perpendicularlyto the longitudinal cutting direction T_(Y).

The mobile means 4 of transverse cutting can be a unit of mobilecutting, which is driven by a motor 6 and brought into alignment withthe desired cutting line T_(X) by means of a motor 5, according todeviation signals provided by the microprocessor. Being so controlled,the motor 5 determines an angular shift of the cutting path, e.g. forthe correction of an oblique trend. To this purpose, while an end of thesliding guide of the cutter 14 is movable in the double directionclockwise/counterclockwise of arrow F′, under the action of the motor 5,the other end is stationary and advantageously serves as a pivot for theresulting rotation.

It will be noted that the above mentioned angular shift occurssimultaneously with the cutting or, based on stored data, alwaysavailable, immediately before the cutting itself. Such a continuousavailability of the correction data and substantial simultaneity betweenshift and cutting operation results to be a peculiar feature of themethod of the invention.

The exact position where the horizontal cut is to be effected can bedetermined either by means of suitable sensors which detect the feedentity of web or sheet 10, or directly by the user of the device.

The cutting is carried out upon alignment of the cutting unit 4 with thetransverse direction T_(X) with respect to the forward feed direction Fof the web.

Contrary to the prior art, according to the method of present inventionthe transverse direction cut can be obtained with an apparatus that doesnot comprise means 3, 3′ for determining the cutting line T_(X),suitable to determine a correct cutting line T_(X) in a directiontransverse to the web feed direction F by detecting one or morereference marks between two subsequent images on the substrate. Such anapparatus is for example described in the patent EP 0 951 973, wherein apair of optical sensors 3,3′ is in particular positioned incorrespondence of two different cross-sections, having a reduceddiameter, of the counter-rotating rollers, and can detect a mark (notshown) provided between two subsequent images printed on the web 10.

1. A method of cutting, simultaneously on two axes perpendicular to eachother, of a substrate with series of images, comprising the steps of:feeding forward the substrate to a flow direction; determining a correctcutting line in a transverse direction to the feed direction of thesubstrate; aligning suitable transverse mobile cutting means with thecutting line by means for shifting the transverse mobile cutting means;cutting the substrate in the transverse direction to the feed directionthereof by said transverse mobile cutting means; detecting a position ofreference marks on the transverse direction to the feed direction of thesubstrate by means of detecting means; forwarding from the detectingmeans a direction signal to a microprocessor; determining through themicroprocessor correct cutting lines in a longitudinal direction withrespect to the feed direction of the substrate; controlling by themicroprocessor by a shifting means to shift longitudinal cutting meansin a direction transverse to the feed direction of the substrate;cutting the substrate in the longitudinal direction along said cuttinglines by said longitudinal cutting means; wherein the step ofcontrolling said shifting means is carried out as a function of speed atwhich the substrate is fed forward and of a speed at which a distancevaries between a reference mark of an image and an ideal feed direction;and the step of determining a correct cutting line in the transversedirection to the feed direction of the substrate comprises theoperations of: detecting the speed at which the substrate is fed and thespeed at which the distance varies between the reference mark of theimage and the ideal feed direction; and determining a correct cuttingline in a transverse direction to the feed direction of the substrate bydata processing according to trigonometric relations by means of saidmicroprocessor to obtain the angle of parallelism defect of the imagewith respect to the ideal feed forward direction.
 2. The method ofcutting according to claim 1, wherein each reference mark isdelimitation line between zones having a sufficient contrast withrespect to each other.
 3. The method of cutting according to claim 1,wherein each reference mark is a single line or multiple lines printedparallel to an edge of the image.
 4. The method of cutting according toclaim 1, wherein each reference mark is an edge of the image when acontrast between a color of the substrate and a color of the edge of theimage is sufficient for the detecting means to detect the edge of theimage.
 5. The method of cutting according to claim 1, wherein eachreference mark is an edge of the substrate, when the image referencemark is substantially parallel to an edge of the image.
 6. The method ofcutting according to claim 1, wherein the shifting of the transversemobile cutting means and the longitudinal cutting means takes place at asame time as the cutting step.
 7. The method of cutting according toclaim 1, wherein the shifting of the transverse mobile cutting means andthe longitudinal cutting means takes place immediately before saidcutting step, with correction data being continuously stored andavailable.